For me, the main point of friendship is to understand people. I get a lot out of learning people, and just as much out of them learning me. It's almost a sensual pleasure, like someone lovingly petting my brain (when they learn me), or wandering through someone else's garden exploring and smelling and seeing and tasting (when I learn them). So each interaction is its own little world, and has its own purpose for existence. In this way I never regret investing in anyone, even if they turn cruel and hurt me on purpose, or even if I never meet them again; those experiences still exist and they formed pathways in my mind that cannot be undone.
I've been thinking about closeness as it relates to time and distance. Some people I can talk to sporadically with gaps of months even, but always feel at a similar level of closeness with. But with others, I do not feel close at all if we don't see each other regularly and talk often. On reflection, I have realized that when I feel closeness despite time lapse and distance is when I have a connection with someone who is in a stable place in their lives -- when we come back together after a time apart, there have been events that passed, but the person is on the same basic trajectory, and I still know their wavelengths enough to harmonize with them. When the person is in a period of great upheaval, or when they have a fairly chaotic trajectory, I feel distant from them very fast, and it feels difficult to find a harmonizing wavelength when we reconnect. I feel a great loss at this, because of all the harmonizing that could have happened, and didn't, and can't ever come back. I also feel fear, because what if we no longer can harmonize at all because we have become too different? So far that fear has never come true, but it remains.
Also, when I get used to being aware of all the small fluctuations in someone's wavelength and then I miss a bunch (such as when I connect with someone every day for a month and then not at all for a week), I feel quite jarred when they are not where I expect them to be the next time we connect. I then have a similar feeling to when I've missed greater changes, because the little ones became important to my life. If this happens over and over, I stop wanting to be close in a daily or continuous way because that jarring feeling is really upsetting, and I begin to dread it.
Relatedly, this has been the pattern at the end of several of my romantic relationships. Daily/continuous closeness is a vital part of romantic feeling for me, and lack of that means that I might feel occasional bursts of romantic love, but it's not the same as being in love. Continuous closeness isn't the only thing needed for me to feel romantic love but it is an essential part. I need that harmonizing feeling to sustain my romance. I need to not dread the 'drop' and I need to not have to spend so much energy getting back in sync.
What else do I need to feel romantic love? 1) mutual desire/effort for closeness and 2) kisses and/or effusive honest verbal expressions of love and 3) the choice to feel it (which depends on a kind of certainty I can't explain). I had a very romantic friendship with Hannah long before we had a sensual/sexual relationship, because sexual desire is a completely separate thing from romantic love, for me. It's basically something I can switch on (initially) for anyone I please, and can almost always switch off for anyone I please. I choose to switch it on when I feel it would make my romantic relationship more intimate and joyous, or when I want to be closer to someone and they aren't skilled at non-sexual intimacy (much less common, but has happened once or twice). I switch it off -- or, more accurately, hold it at the off position -- when sex would possibly cause a painful situation (such as when I was first getting close to Topaz and was sure that ze was not down with dating a poly person).